In an electric vehicle, a so-called automotive power electronics system for obtaining mechanical energy from electric energy primarily includes a battery for supplying a direct current power supply, a power conversion device for converting direct current to alternating current, such as an inverter, and a motor for obtaining a turning force from an electrical output of the power conversion device.
The motor obtains a turning force from alternating current electricity outputted from the power conversion device by electromagnetic effects.
The power conversion device is connected to the battery through shielded cables. A casing of the power conversion device contains a switch group (power module), including modularized power semiconductor elements, and a capacitor. Here, in the power conversion device, plate-shaped conductors (bus bars) are provided to connect the power module and the shielded cables extending from the battery, and the capacitor is a smoothing capacitor which absorbs fluctuations in input voltage to the power conversion device. This smoothing capacitor is connected to power supply buses connecting the battery and the power conversion device, and partly reduces voltage fluctuations generated by switching. Moreover, the casing of the power conversion device contains a control circuit which controls the rotation of the motor by opening or closing the switch group including power semiconductor elements.
The power conversion device having the above-described configuration opens or closes the switch group according to a signal from the control circuit, thus converting direct current electricity of the battery to generate alternating current electricity for obtaining the turning force of the motor.
In a power conversion device such as described above, when switches disposed therein are opened or closed, switching noise is generated. When it is assumed that the power conversion device is mounted on, for example, a vehicle, this switching noise affects listening to a mobile radio mounted on the vehicle, e.g., makes it difficult to listen to the radio or generates grating noise. In some cases, there is concern that this switching noise may also inversely affect the operations of other digital instruments mounted on the vehicle.
Accordingly, as a conventional technique for reducing a surge voltage generated by switching, Patent Literature 1 has been disclosed. In this Patent Literature 1, in a semiconductor device to be used in a power conversion device, an electrode connected to a positive side of a power supply and an electrode connected to a negative side of the power supply are disposed parallel, and configured such that currents flow through the electrodes in opposite directions, respectively. Thus, magnetic fluxes generated by the currents cancel out each other, and inductance is reduced. Accordingly, the surge voltage generated by switching is reduced.